FIG. 1 is a schematic block diagram of a communication system comprising a host terminal 2 and an external wireless cellular modem 4, the modem 4 comprising an antenna 5. The host terminal 2 may be a user terminal, and may for example take the form of a desktop computer, laptop computer, tablet style computer, or mobile phone (which may be referred to as a “smart phone”). The modem 4 may for example take the form of a dongle for plugging into the host terminal 2. Alternatively the modem 4 may take the form of a mobile phone handset which, as well as being a conventional mobile telephone, can be connected to the host terminal 2 so as to act as an external cellular modem for the host terminal 2. The modem 4 is external to the host terminal 2 in that it is a separate unit housed in a separate casing, but which is connected or connectable to the host terminal 2 by means of a wired or wireless connection (as well as being removable or being able to be disconnected from the host terminal 4). In another alternative set up, the modem 4 could be internal to the terminal 4, e.g., taking the form of a wireless module in a desktop or laptop computer.
The system also comprises a mobile cellular network 6 such as a 3GPP network; and a further, packet-based network 8, such as, a wide area internetwork such as the Internet. The networks are coupled together by one or more gateway routers (not shown). The mobile network 6 comprises a plurality of antennas 10 and a gateway support entity 7 operatively coupled to the gateway routers and the plurality of antennas. For example the gateway support entity may be a GGSN (Gateway GPRS Support Node) in a 2G or 3G system, or an SAE (System Architecture Evolution) gateway in a LTE (Long Term Evolution) system. The GGSN 7 or other such gateway support entity is configured to provide one or more access points 12 which enable a terminal such as the host terminal 2 to access the Internet 8 via the mobile network 6. Each of the access points 12 has a respective name which is used by a terminal 2 and modem 4 to request use of the access point for accessing the Internet 8. The name of an access point may be referred to as the APN (access point name), and the term APN is sometimes used interchangeably with reference to the access point itself. An APN maps to a specific gateway to a specific PDN (packet data network), for a specific service (e.g. Web browsing, MMS or WAP). Several APNs may map to the same gateway. The APN is a name of the gateway or the gateway itself. The gateway may have several names. The APN corresponds to a specific service or a set of services that are provided by one unique gateway.
For connecting to the 3GPP network 6 or other such cellular network, the modem 4 comprises first physical interface apparatus comprising a wireless transceiver, typically in the form of a radio frequency (RF) transceiver and an antenna 5. This interface apparatus of the modem 4 connects via an antenna 10 to the cellular network 6, enabling the modem 4 to establish a channel 20 between itself and one of the access points 12 provided by the GGSN7 of the cellular network 6. This channel may be referred to as a “context”. For example, if the mobile cellular network 6 is a 3GPP network, then the connection between the modem 4 and a 3GPP network 6 may be called a PDP (Packet Data Protocol) context in 2G or 3G terminology, and an EPS (Evolved Packet System) bearer context in LTE (Long Term Evolution standards) terminology. The context 20 comprises parameters for establishing the connection with the access point 12, such as context type, quality-of-service (QoS) parameters, authentication type and information of a domain name system. The physical medium of the connection is typically a radio channel such as a 2G, 3G or LTE radio channel and the protocol that drives it may comprise a set of protocol layers as defined for example by 3GPP. Each of the one or more access points 12 connects on to a router of the Internet 8. The first router encountered on the route onwards from the mobile cellular network 6, i.e. the router immediately connecting to the access point 12, is the gateway between the cellular network 6 and the Internet 8.
For connecting to the host terminal 2, the modem 4 comprises second physical interface apparatus. The second interface, between the host 2 and modem 4, could for example comprise a wired connection such as USB, or a short-range wireless transceiver such as an infrared connection or a radio frequency connection (e.g. Bluetooth).
The host terminal 2 is installed with one or more applications 18 which when executed on the host terminal 2 send and/or receive communications over the Internet 8 via the first and second interface apparatuses, wireless cellular network 6, access point 12 and the relevant gateway, over the established context 20, supported by the GGSN 7. The system allows the host terminal to access the Internet 8 using a suitable packet protocol or communication protocol stack comprising one or more packet protocol layers implemented at the modem 4 and at one or more nodes of the mobile network 6 and Internet 8, e.g. using an Internet Protocol version 6 (IPv6) stack and/or Internet Protocol version 4 (IPv4) stack. The host terminal 2 may be installed with and run one or more applications 18i that operate exclusively based on use of IPv4, one or more applications 18ii that operate exclusively based on use of IPv6, and/or one or more applications 18i configured to make use of a mixture of IPv4 and IPv6 features (“dual-stack connectivity”). To this end, the modem 4 may be operable to establish a context 20i of a type which operates exclusively based on IPv4, to establish a context 20ii of a type which operates exclusively based on IPv6, and/or to establish a context 20iii of a type which can support both IPv4 and IPv6.
Reference is made to 3GPP TS 23.003 section 9.1, 3GPP TS 23.060 section 9.2.1 and 3GPP TS 27.007 section 10.1.1.